Thrust efficient turbofan engine

ABSTRACT

A disclosed turbofan engine includes a gas generator section for generating a gas stream flow and a propulsor section for generating propulsive thrust as a mass flow rate of air through a bypass flow path. The propulsor section includes a fan driven by a power turbine through a speed reduction device at a second rotational speed lower than a first rotational speed of the power turbine. An Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of the mass flow rate of air through the bypass flow path, a tip diameter of the fan and the first rotational speed of the power turbine is between 0.05 and 0.13 during operation of the turbofan engine.

REFERENCE TO RELATED APPLICATION

The present disclosure is a continuation of U.S. application Ser. No.14/497,822 that is a continuation-in-part of U.S. application Ser. No.13/854,225 filed on Apr. 1, 2013, now U.S. Pat. No. 9,624,827 granted onApr. 18, 2017, which claims priority to U.S. Provisional Application No.61/787,321 filed on Mar. 15, 2013. U.S. application Ser. No. 14/497,822also claims priority to U.S. Provisional Application No. 62/884,327filed on Sep. 30, 2013

BACKGROUND

A turbofan engine typically includes a fan section, a compressorsection, a combustor section and a turbine section. Air entering thecompressor section is typically compressed and delivered into thecombustor section where it is mixed with fuel and ignited to generate ahigh-pressure, high-temperature gas flow. The high-pressure,high-temperature gas flow expands through the turbine section to drivethe compressor and the fan section.

A direct-drive turbofan engine typically includes a fan section directlydriven by a low pressure turbine producing the power needed to drive thefan section, such that the low pressure turbine and the fan sectionrotate at a common rotational speed in a common direction. A powertransmission device such as a gear assembly or other mechanism may beutilized to drive the fan section such that the fan section may rotateat a speed different than the turbine section so as to increase theoverall efficiency of the engine. In a gear-drive turbofan enginearchitecture, a shaft driven by one of the turbine sections may providean input to the speed reduction device that drives the fan section at areduced speed such that both the turbine section and the fan section canrotate at closer to their respective optimal rotational speeds.

SUMMARY

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a gas stream flow with higher energy per unit mass flowthan that contained in ambient air. A power turbine configured forconverting the gas stream flow into shaft power. The power turbineconfigured for rotating at a first rotational speed and operating at atemperature less than about 1800° F. at a sea level takeoff powercondition. A speed reduction device configured to be driven by the powerturbine. A propulsor section includes a fan configured to be driven bythe power turbine through the speed reduction device at a second speedlower than the first speed for generating propulsive thrust as a massflow rate of air through a bypass flow path. The engine is configuredsuch that when operating at the sea level takeoff power condition abypass ratio of a first volume of air through the bypass flow pathdivided by a second volume of air directed into the gas generator isgreater than about 10.0 and a pressure ratio across the fan is less thanabout 1.50.

In a further embodiment of the foregoing turbofan engine, the fanincludes a tip diameter greater than about fifty (50) inches and anEngine Unit Thrust Parameter (“EUTP”) defined as net engine thrustdivided by a product of the mass flow rate of air through the bypassflow path, a tip diameter of the fan and the first rotational speed ofthe power turbine is less than about 0.30 at the sea level takeoff powercondition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.25 at the take-take off condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP is less than about 0.20 at the takeoff condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.10.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.08.

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is greater than about 50 inches and less thanabout 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/sec and about 80,000 lbm/sec.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the power turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thepropulsive thrust generated by the turbofan engine is between about16,000 lbf and about 120,000 lbf.

In a further embodiment of any of the foregoing turbofan engines, thegas generator defines an overall pressure ratio of between about 40 andabout 80.

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a gas stream flow with higher energy per unit mass flowthan that contained in ambient air. A power turbine for converting thegas stream flow into shaft power. The power turbine is rotatable at afirst rotational speed, wherein the power turbine operates at atemperature less than about 1800° F. at a sea level takeoff powercondition. A speed reduction device is configured to be driven by thepower turbine. A propulsor section includes a fan configured to bedriven by the power turbine through the speed reduction device at asecond speed lower than the first speed for generating propulsive thrustas a mass flow rate of air through a bypass flow path. The fan includesa fan tip diameter greater than about fifty (50) inches and an EngineUnit Thrust Parameter (“EUTP”) defined as net engine thrust divided by aproduct of the mass flow rate of air through the bypass flow path, a tipdiameter of the fan and the first rotational speed of the power turbineis less than about 0.30 at the sea level takeoff power condition and orabout 0.15 at one of a climb condition and a cruise condition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.125 for at least one of the climb condition and thecruise condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of the climb condition and the cruise condition is less thanabout 0.08.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at a takeoff condition is less than about 0.15.

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is between about 50 inches and about 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/sec and about 80,000 lbm/sec.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the power turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thepropulsive thrust generated by the turbofan engine is between about16,000 lbf and about 120,000 lbf.

In a further embodiment of any of the foregoing turbofan engines, thegas generator defines an overall pressure ratio of between about 40 andabout 80.

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a high energy gas stream. The gas generating sectionincludes a compressor section, combustor section and a first turbine. Asecond turbine converts the high energy gas stream flow into shaftpower. The second turbine rotates at a first speed and includes lessthan or equal to about six (6) stages. A geared architecture is drivenby the second turbine. A propulsor section is driven by the secondturbine through the geared architecture at a second speed lower than thefirst speed. The propulsor section includes a fan with a pressure ratioacross the fan section less than about 1.50. The propulsor sectiongenerates propulsive thrust as a mass flow rate of air through a bypassflow path from the shaft power. The fan includes a tip diameter greaterthan about fifty (50) inches and an Engine Unit Thrust Parameter(“EUTP”) defined as net engine thrust divided by a product of a massflow rate of air through the bypass flow path, a tip diameter of the fanand the first rotational speed of the second turbine is less than about0.30 at a takeoff condition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.25 at the takeoff condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP is less than about 0.20 at the takeoff condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.10.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at the takeoff condition is less than about 0.08.

In a further embodiment of any of the foregoing turbofan engines, thefan section defines a bypass airflow having a bypass ratio greater thanabout ten (10).

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is between about 50 inches and about 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/sec and about 80,000 lbm/sec.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the second turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thesecond turbine comprises a low pressure turbine with 3 to 6 stages.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example turbofan engine.

FIG. 2 is a schematic view of functional elements of the exampleturbofan engine.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes a fan section 22, a compressor section 24, a combustor section26 and a turbine section 28. Alternative engines might include anaugmenter section (not shown) among other systems or features. The fansection 22 drives air through a bypass flow path B while the compressorsection 24 draws air in along a core flow path C where air is compressedand communicated to a combustor section 26. In the combustor section 26,air is mixed with fuel and ignited to generate a high pressure exhaustgas stream that expands through the turbine section 28 where energy isextracted and utilized to drive the fan section 22 and the compressorsection 24.

Although the disclosed non-limiting embodiment depicts a two-spoolturbofan gas turbine engine, it should be understood that the conceptsdescribed herein are not limited to use with two-spool turbofans as theteachings may be applied to other types of turbine engines; for examplea turbine engine including a three-spool architecture in which threespools concentrically rotate about a common axis and where a low spoolenables a low pressure turbine to drive a fan via a speed reductiondevice such as a gearbox, an intermediate spool that enables anintermediate pressure turbine to drive a first compressor of thecompressor section, and a high spool that enables a high pressureturbine to drive a high pressure compressor of the compressor section.

The example engine 20 generally includes a low speed spool 30 and a highspeed spool 32 mounted for rotation about an engine central longitudinalaxis A relative to an engine static structure 36 via several bearingsystems 38. It should be understood that various bearing systems 38 atvarious locations may alternatively or additionally be provided and thatthe location of the bearing systems 38 may be varied as appropriate tothe application.

The low speed spool 30 generally includes an inner shaft 40 thatconnects a fan 42 and a low pressure (or first) compressor section 44 toa low pressure (or first) turbine section 46. The inner shaft 40 drivesthe fan 42 through a speed change device, such as a geared architecture48, to drive the fan 42 at a lower speed than the low speed spool 30.The high-speed spool 32 includes an outer shaft 50 that interconnects ahigh pressure (or second) compressor section 52 and a high pressure (orsecond) turbine section 54. The inner shaft 40 and the outer shaft 50are concentric and rotate via the bearing systems 38 about the enginecentral longitudinal axis A.

A combustor 56 is arranged between the high pressure compressor 52 andthe high pressure turbine 54. In one example, the high pressure turbine54 includes at least two stages to provide a double stage high pressureturbine 54. In another example, the high pressure turbine 54 includesonly a single stage. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine. It will be appreciated that each of thepositions of the fan section 22, compressor section 24, combustorsection 26, turbine section 28, and fan drive gear system 48 may bevaried. For example, gear system 48 may be located aft of combustorsection 26 or even aft of turbine section 28, and fan section 22 may bepositioned forward or aft of the location of gear system 48.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about five (5). The pressure ratio of the example low pressureturbine 46 is measured prior to an inlet of the low pressure turbine 46as related to the pressure measured at the outlet of the low pressureturbine 46 prior to an exhaust nozzle.

A mid-turbine frame 58 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 58 further supports bearing systems 38in the turbine section 28 as well as setting airflow entering the lowpressure turbine 46.

Airflow through the core airflow path C is compressed by the lowpressure compressor 44 then by the high pressure compressor 52 mixedwith fuel and ignited in the combustor 56 to produce a gas stream withhigh energy that expands through the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 58 includes vanes 60, whichare in the core airflow path C and function as an inlet guide vane forthe low pressure turbine 46. Utilizing the vane 60 of the mid-turbineframe 58 as the inlet guide vane for low pressure turbine 46 decreasesthe length of the low pressure turbine 46 without increasing the axiallength of the mid-turbine frame 58. Reducing or eliminating the numberof vanes in the low pressure turbine 46 shortens the axial length of theturbine section 28. Thus, the compactness of the gas turbine engine 20is increased and a higher power density may be achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example speedreduction device is a geared architecture 48 however other speedreducing devices such as fluid or electromechanical devices are alsowithin the contemplation of this disclosure. The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 1.8 and, in some embodiments,greater than about 4.5.

In one disclosed embodiment, the gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of the low pressurecompressor 44. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a gas turbine engineincluding a geared architecture and that the present disclosure isapplicable to other gas turbine engines. A significant amount of thrustis provided by airflow through the bypass flow path B due to the highbypass ratio. The fan section 22 of the engine 20 is designed for aparticular flight condition—typically cruise at about 0.8 Mach and about35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., with theengine at its best fuel consumption—also known as “bucket cruise ThrustSpecific Fuel Consumption (‘TSFC’)”—is the industry standard parameterof pound-mass (lbm) of fuel per hour being burned divided by pound-force(lbf) of thrust the engine produces at that minimum point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodiment,the low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram °R)/(518.7° R)]^(0.5). The “Low corrected fan tip speed”, as disclosedherein according to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about twenty-six (26) fan blades. Inanother non-limiting embodiment, the fan section 22 includes less thanabout twenty (20) fan blades. Moreover, in one disclosed embodiment thelow pressure turbine 46 includes no more than about six (6) stagesschematically indicated at 34. In another non-limiting exampleembodiment, the low pressure turbine 46 includes about three (3) stages.A ratio between the number of fan blades 42 and the number of lowpressure turbine rotors is between about 3.3 and about 8.6. The examplelow pressure turbine 46 provides the driving power to rotate the fansection 22 and therefore the relationship between the number of stages34 in the low pressure turbine 46 and the number of blades 42 in the fansection 22 defines an example gas turbine engine 20 with increased powertransfer efficiency.

Referring to FIG. 2, with continued reference to FIG. 1, the exampleturbofan engine 20 includes a gas generator section 62 for generating ahigh energy (per unit mass) gas stream 78. A power turbine 76 convertsthe high energy gas stream 78 into shaft power that drives the gearedarchitecture 48. In one embodiment, the power turbine may be the lowpressure turbine 46 that drives the inner shaft 40. The power turbine 76drives a propulsor section 64 through the geared architecture 48. Thepropulsor section 64 generates a mass flow 70 of air through the bypassflow path B that is a substantial portion of the overall propulsivethrust 68 generated by the turbofan engine 20.

The gas generator section 62 includes part of the fan sectioncompressing the air flow directed along the core flow path C, the lowpressure compressor 44, the high pressure compressor 52, the combustor56, the high pressure turbine 54 and part of the low-pressure turbine46. The high pressure turbine 54 is the first turbine after thecombustor 56 and drives the high pressure compressor 52. Disclosedexample gas generators include an overall pressure ratio betweenentering airflow and the exiting gas stream of between about 40 and 80.

The power driving the geared architecture 48 and thereby the propulsorsection 64 is provided by the power turbine 76. In this disclosure, thepower turbine 76 comprises the second turbine downstream of thecombustor 56 such as the low pressure turbine 46. The low pressureturbine 46 rotates at the first speed 72 and includes no more than six(6) stages 34. Moreover, the low pressure turbine 46 may include betweenthree (3) and six (6) stages 34, inclusive.

The power or low pressure turbine 46 rotates at the first speed 72(measured in terms of revolutions per minute) greater than a secondspeed 74 (also measured in terms of revolutions per minute) at which thefan section 22 rotates. In some embodiments, the first speed may bebetween about 6200 rpm and about 12,500 rpm. The first speed of the lowpressure turbine 46 is enabled by the speed reduction provided by thegeared architecture 48. At the first speed 72, each of the stages 34 aremore efficient at converting energy from the gas flow 78 to powertransmitted through the inner shaft 40.

The power turbine 76 operates at a more efficient speed and thereforemay operate at a more efficient temperature, schematically indicated at75, for converting energy from the gas flow 78 to power through theinner shaft 40. In one example embodiment, the power turbine 76 operatesat temperatures below about 1800° F. during a sea level takeoff powercondition with an ambient temperature of about 86° F. The sea leveltakeoff power condition, during the day and at 86° F. is a standardcondition utilized to measure and compare engine performance.

In this example, the power turbine temperature is determined with theengine 20 at the sea level takeoff power setting in a static uninstalledcondition. The static and uninstalled condition is with the engineoperating during test conditions while not subject to parasitic lossessuch as providing cabin bleed air to an aircraft cabin. In anotherexample embodiment, the power turbine 76 operates at temperatures belowabout 1760° F. during the same seal level takeoff power condition withan ambient temperature of about 86° F. in a static uninstalledcondition.

The propulsor section 64 includes the fan section with fan blades 42that rotate about the engine axis A. The fan blades 42 extend radiallyoutward to define a tip diameter 66 between tips of opposing blades 42.The disclosed fan section 22 includes a tip diameter 66 that, in someembodiments, may be between about 45 inches (114 cm) and about 160inches (406 cm). In another example embodiment, the tip diameter 66 isbetween about 50 inches (127 cm) and about 85 inches (215.9 cm). The tipdiameter of the fan section 22 enables the desired fan pressure ratio incombination with the second rotational speed 74 provided by the gearreduction of the geared architecture 48.

The propulsor section 64 includes the fan section 22, and also includesthe fan exit guide vanes 80 and typically a fan nozzle 82. The fansection 22 is rotated at the second speed 74 by the geared architecture48 at a speed determined to enable the generation of the mass flow 70through the bypass flow path B. The pressure ratio across the fansection enables the efficient transformation of the shaft power providedin the power turbine 76 to propulsive thrust.

Fan pressure ratios below about 1.5, and better below 1.45 enabledesirable generation of thrust. The desired fan pressure ratio can beobtained utilizing a combination of fan exit guide vanes 80 and the fannozzle 82 that cooperate with the fan section 22 to enable fan pressureratios of less than 1.45. The mass flow 70 produced by the examplepropulsor section 64 may, in some embodiments, be between about 625lbm/sec (283 kg/sec) and about 80,000 lbm/sec (36,287 kg/sec). The massflow of air 70 through the bypass flow path B combines with thrustgenerated by gas flow 78 to provide the overall engine thrust 68.However, a majority of engine thrust is provided by the mass flow of air70 generated by the propulsor section 64.

The overall efficiency of the turbofan engine 20 is a combination of howwell each of the sections 62, 76 and 64 converts input energy into thedesired output. The gas generator section 62 transforms energy from theair/fuel mixture ignited in the combustor 56 into the high-energy gasstream 78. The power turbine 46 converts energy from the gas stream 78into shaft power rotating the inner shaft 40 at a first speed 72 todrive the propulsor 64. The propulsor section 64 generates the mass flowof air 70 through bypass flow path B that provides the propulsive thrust68.

The thrust generation efficiency of the engine is related to the EngineUnit Thrust Parameter (“EUTP”), which is defined as the net thrustproduced by the engine divided by the product of mass flow rate of airthrough the fan bypass section, the fan tip diameter and the rotationalspeed of the power turbine section, as set out in Equation 1.

$\begin{matrix}{{{{{Engine}\mspace{14mu}{Unit}\mspace{14mu}{Thurst}\mspace{14mu}{Parameter}} =}\quad}\frac{{Not}\mspace{14mu}{Thrust}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{Engine}}{\begin{bmatrix}\left( {{mass}\mspace{14mu}{flow}\mspace{14mu}{rate}\mspace{14mu}{of}\mspace{14mu}{air}\mspace{14mu}{through}\mspace{14mu}{fan}\mspace{14mu}{bypass}} \right) \\\begin{matrix}\left( {{Fan}\mspace{14mu}{Tip}\mspace{14mu}{Diameter}} \right) \\\left( {{Speed}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{power}\mspace{14mu}{turbine}} \right)\end{matrix}\end{bmatrix}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The EUTP is a dimensionless quantity calculated utilizing the net enginethrust, the mass flow rate of air, the tip diameter and the powerturbine rotational speed expressed in appropriate units. For example, ifthe SI system of units is used, the units for these four quantities willbe N, kg/s, m and radians/s, respectively. The calculation of the EUTPwill be straight forward with no need to use conversion factors. If a“customary” set of units are used, i.e., engine thrust expressed in lbf,mass flow rate expressed in lbm/s, fan diameter express in inches androtational speed expressed in RPM, then the ratio calculated using thesevalues are multiplied by constant approximately equal to 3686.87 toaccount for all conversion factors necessary to get all parameters inself-consistent units.

Embodiments of the geared gas turbine engine 20 including the disclosedfeatures and configurations produce thrust ranging between about 16,000lbf (71,171 N) and about 120,000 lbf (533,786 N). The EUTP for thedisclosed turbofan engine 20 is less than those provided in prior artturbine engines. Three disclosed exemplary engines which incorporatepower turbine and propulsor sections as set forth in this applicationare described and contrasted with prior art engine examples in Table 1.

TABLE 1 Prior Art Prior Art Engine 1 Engine 2 Engine 3 Engine 1 Engine 2Fan Diameter in 55.9 73.0 81.0 63.5 49.2 Thrust Class lbf 17K 23.3K 33K33K 21K Max Climb Thrust lbf 3526 4878 6208 9721 8587 Fan face corr.Flow lbm/sec 703.4 1212.1 1512.4 847.0 502.6 Fan OD corr. Flow lbm/sec626.3 1108.8 1388.6 696.4 314.2 Fan face physical flow lbm/sec 261.5450.6 561.7 519.4 308.8 Fan OD physical flow lbm/sec 232.7 412.1 515.6426.9 193.1 Second speed (fan) RPM 4913 3377 3099 4969 7640 First speed(power turbine) RPM 11835 10341 9491 4969 7640 Engine Unit ThrustParameter 0.08 0.06 0.06 0.27 0.44 Average Cruise Thrust lbf 2821 39294729 5300 4141 Fan face corr. Flow lbm/sec 668.3 1157.6 1429.4 845.6490.5 Fan OD corr. Flow lbm/sec 598.0 1065.6 1322.6 695.5 312.1 Fan facephysical flow lbm/sec 254.1 440.2 543.4 327.4 181.1 Fan OD physical flowlbm/sec 227.3 405.2 502.7 269.2 115.2 Second speed (fan) RPM 4472 30702748 4769 6913 First speed (power turbine) RPM 10774 9402 8416 4769 6913Engine Unit Thrust Parameter 0.08 0.05 0.05 0.24 0.39 Max Takeoff Thrustlbf 12500 18735 25678 25382 17941 Fan face corr. Flow lbm/sec 610.01032.5 1438.8 871.1 496.6 Fan OD corr. Flow lbm/sec 546.6 948.5 1330.2711.8 312.1 Fan face physical flow lbm/sec 611.0 1029.4 1452.2 901.5509.4 Fan OD physical flow lbm/sec 547.4 945.6 1342.4 736.1 320.2 Secondspeed (fan) RPM 4689 3249 3117 5411 7791 First speed (power turbine) RPM11295 9951 9546 5411 7791 Engine Unit Thrust Parameter 0.13 0.10 0.090.37 0.54

In some example embodiments, the EUTP is as low as 0.05 at a cruisecondition and less than about 0.10 at maximum takeoff thrust. In anotherengine embodiment including a fan tip diameter greater than about fifty(50) inches the EUTP is less than about 0.30 at maximum takeoff thrust.In another engine embodiment including the fan tip diameter greater thanabout fifty (50) inches, the EUTP is less than about 0.25. In still afurther engine embodiment including a fan tip diameter greater thanabout fifty (50) inches, the EUTP is less than about 0.20.

In a further embodiment, the EUTP is less than about 0.08 at a takeoff,cruise and/or a climb condition. In one engine embodiment including afan tip diameter greater than about fifty (50) inches, the EUTP is lessthan about 0.15 at a cruise and/or climb condition. In another engineembodiment including a fan tip diameter of greater than about fifty (50)inches, the EUTP is less than about 0.125 at a cruise and/or climbcondition.

Moreover, the EUTP is accomplished through the use of the gearedarchitecture 48 at a gear ratio of, in some embodiments, greater thanabout 2.3. In other embodiments, the gear ratio may be greater thanabout 2.8. Accordingly, a ratio of the EUTP to the gear ratio furtherdefines physical operating characteristics of the disclosed engines. Inone disclosed embodiment, a ratio of the EUTP at takeoff to a gear ratioof 2.8 is about 0.028. In another disclosed ratio of the EUTP at a climbor cruise condition to the gear ratio of 2.8 is between about 0.036 and0.054.

Accordingly, the EUTP for engines based upon the disclosed features maybe less than 0.30 when the engine is operating at takeoff condition,while it may have a value less than 0.1 when operating at climb andcruise conditions.

Accordingly, the disclosed embodiments of each of the gas generator 62,power turbine 76 and propulsor sections 64 of the geared engineembodiments efficiently convert energy to provide a more thrustefficient turbofan engine as compared to conventional non-gearedengines.

Although various example embodiments have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this disclosure. For that reason, thefollowing claims should be studied to determine the scope and content ofthis disclosure.

What is claimed is:
 1. A turbofan engine comprising: a propulsor sectionincluding a fan and a bypass flow path, wherein the fan includes anumber of fan blades that each have a fan tip diameter greater than 50inches and less than 160 inches; a compressor section including a lowpressure compressor and a high pressure compressor; a turbine sectionincluding a high pressure turbine coupled to the high pressurecompressor and a power turbine coupled to the low pressure compressor,wherein the power turbine rotates at a first rotational speed between8,416 rpm and 11,835 rpm during engine operation; a geared architecturedefining a driving connection between the power turbine and the fanwherein a net engine thrust is between 16,000 lbf and 120,000 lbf, amass flow rate of air through a bypass flow passage is between 625lbm/sec and 80,000 lbm/sec; and an Engine Unit Thrust Parameter (“EUTP”)defined as net engine thrust divided by a product of a mass flow rate ofair through the bypass flow path, the fan tip diameter of the fan andthe first rotational speed of the power turbine in operation is between0.05 and 0.13.
 2. The turbofan engine as recited in claim 1, wherein aspeed reduction ratio provided by the geared architecture between thefan and the power turbine is between 1.8 and 4.5.
 3. The turbofan engineas recited in claim 2, wherein the speed reduction ratio is between 2.3and 2.8.
 4. The turbofan engine as recited in claim 2, furthercomprising a low fan pressure ratio across the fan alone that is greaterthan zero and less than 1.50.
 5. The turbofan engine as recited in claim4, wherein the high pressure turbine includes at least one stage and nomore than two stages.
 6. The turbofan engine as recited in claim 5,wherein the high pressure turbine comprises a two-stage high pressureturbine.
 7. The turbofan engine as recited in claim 5, wherein the highpressure turbine comprises a one-stage high pressure turbine.
 8. Theturbofan engine as recited in claim 5, wherein the power turbinecomprises at least 3 stages and no more than 6 stages and a ratiobetween the number of fan blades and the number of stages in the powerturbine is between 3.3 and 8.6.
 9. The turbofan engine as recited inclaim 8, wherein the number of fan blades is less than
 20. 10. Theturbofan engine as recited in claim 9, further including a mid-turbineframe disposed between the high pressure turbine and the power turbine,the mid-turbine frame including an inlet guide vane for directing a gasstream from the high pressure turbine into the power turbine.
 11. Theturbofan engine as recited in claim 10, further comprising a gasgenerator section, the gas generation section including a core flow pathportion of the propulsor section through the low pressure compressor,the high pressure compressor, a combustor, the high pressure turbine anda part of the power turbine, the gas generator having an overallpressure ratio between airflow entering the gas generator and a gasstream exiting the gas generator that is between 40 and 80 in operation.12. The turbofan engine as recited in claim 11, wherein the firstrotational speed is greater than 10,000 rpm.
 13. The turbofan engine asrecited in claim 11, wherein the first rotational speed is between 9,400rpm and 10,350 rpm.
 14. The turbofan engine as recited in claim 11,wherein the first rotational speed is greater than 8,416 rpm and lessthan 9,546 rpm.
 15. A turbofan engine comprising: a gas generatorsection generating a gas stream flow with higher energy per unit massflow than that contained in ambient air during engine operation; a powerturbine converting the gas stream flow into shaft power, the powerturbine rotating at a first rotational speed between 8,416 rpm and12,500 rpm during engine operation; a speed reduction device driven bythe power turbine; and a propulsor section including a fan coupled tothe power turbine through the speed reduction device and rotatable at asecond rotational speed lower than the first rotational speed, wherein afan tip diameter of the fan is between fifty (50) and one-hundred sixty(160) inches, a mass flow rate of air through a bypass flow path isbetween 625 lbm/sec and 80,000 lbm/sec and a net engine thrust isbetween 16,000 lbf and 33,000 lbf during engine operation and an EngineUnit Thrust Parameter (“EUTP”), defined as net engine thrust divided bya product of the mass flow rate of air through a bypass flow path, a tipdiameter of the fan and the first rotational speed of the power turbineof the turbofan engine during operation is between 0.05 and 0.13. 16.The turbofan engine as recited in claim 15, wherein a speed reductionratio provided by the speed reduction device is between the fan and thepower turbine is between 2.3 and 4.5.
 17. The turbofan engine as recitedin claim 16, further comprising a low fan pressure ratio across the fanalone that is greater than zero and less than 1.50.
 18. The turbofanengine as recited in claim 17, further comprising a two-stage highpressure turbine.
 19. The turbofan engine as recited in claim 18,wherein the power turbine comprises at least 3 stages and no more than 6stages and a ratio between the number of fan blades and the number ofstages in the power turbine is between 3.3 and 8.6.
 20. The turbofanengine as recited in claim 19, wherein the number of fan blades is lessthan
 20. 21. The turbofan engine as recited in claim 20, furtherincluding a mid-turbine frame disposed between the high pressure turbineand the power turbine, the mid-turbine frame including an inlet guidefan for directing an exhaust gas stream from the high pressure turbineinto the power turbine.
 22. The turbofan engine as recited in claim 21,wherein the gas generator section includes a core flow path portionthrough a low pressure compressor, a high pressure compressor, acombustor, the high pressure turbine and a part of the power turbine,the gas generator having an overall pressure ratio between airflowentering the gas generator and a gas stream exiting the gas generatorthat is between 40 and 80 in operation.
 23. The turbofan engine asrecited in claim 22, wherein the first rotational speed is between 9,400rpm and 11,835 rpm.
 24. The turbofan engine as recited in claim 23,wherein the first rotational speed is no more than 10,774 rpm.
 25. Theturbofan engine as recited in claim 24, wherein the first rotationalspeed is no less than 9,546 rpm.
 26. A turbofan engine comprising: a gasgenerator section defining a core flow path portion through a lowpressure compressor, a high pressure compressor, a combustor a highpressure turbine and a part of a power turbine, the power turbineconverting a gas stream flow with higher energy per unit mass flow thanthat contained in ambient air into shaft power by rotating at a firstrotational speed during engine operation; a speed reduction devicedriven by the power turbine; and a propulsor section including a fandriven by the power turbine through the speed reduction device at secondrotational speed that is less than the first rotational speed, wherein afan tip diameter is between fifty (50) and one-hundred sixty (160)inches, a net engine thrust is between 16,000 lbf and 120,000 lbf, amass flow rate of air through a bypass flow path is between 625 lbm/secand 80,000 lbm/sec, the first rotational speed is between 8,416 rpm and12,500 rpm and an Engine Unit Thrust Parameter (“EUTP”), defined as thenet engine thrust divided by a product of the mass flow rate of airthrough the bypass flow path, the tip diameter of the fan and the firstrotational speed of the power turbine for the turbofan engine is between0.05 and 0.13 during operation of the turbofan engine at one of a climb,cruise and/or takeoff operating condition.
 27. The turbofan engine asrecited in claim 26, wherein a speed reduction ratio between the fan andthe power turbine is between 2.3 and 4.5.
 28. The turbofan engine asrecited in claim 27, wherein the high pressure turbine comprises atwo-stage high pressure turbine.
 29. The turbofan engine as recited inclaim 28, wherein the power turbine comprises at least 3 stages and nomore than 6 stages and a ratio between the number of fan blades and thenumber of stages in the power turbine is between 3.3 and 8.6.
 30. Theturbofan engine as recited in claim 29, further including a mid-turbineframe disposed axially between the high pressure turbine and the powerturbine, the mid-turbine frame including an inlet guide fan fordirecting an exhaust gas stream from the high pressure turbine into thepower turbine.